Modal auxiliary verbs
Problems for students studying modal auxiliary verbs 
This is a difficult topic (just in case you hadn't noticed)
* There are a lot of modals - ten; there are a lot of functions -far more than ten. 
* Most modals have more than one function ; most functions use more than one modal to express them. 
* The names of the functions vary from one text book to another (especially possibility and probability) 
* The names of the functions may not be clear to students! 
  
Overview
Please note that:
	this table is not a complete list of the uses of modal auiliary verbs; it merely shows some common ways of using them
	there is some 'overlap' between different functions - the difference between 'ability', 'possibility' etc is not always clear
	sometimes the choice of function to describe a statement etc may depend on the speaker's precise intention
  
Function 	Modals 	Examples 	Other language 	Notes 	
ability 	can, could 	She can drive.  I could swim when I was five. 	be able to  manage  succeed 		
possibility* 	can, could  may, might 	You can book plane tickets online.  Years ago you could go to America by boat.  There may be life on other planets. 	(It is) possible 		
offer 	can  shall, would 	Can I help you?  Shall I give you a hand?  Would you like me to do that for you? 			
permission 	can, could, may, might, would 	Can I borrow your pen?  Could I borrow your pen?  May I borrow your pen?  I was wondering if I might borrow your pen.  Would you mind if I borrowed your pen?  Would it be possible to borrow your pen? 			
request 	can, could, would, 	Can you let me know as soon as possible?  Could you give me a hand with this?  Would you give me a hand with this? 			
advice 	should, ought 	You should see a doctor.  You ought to speak to David - he's an expert on modal auxiliary verbs. 	had better    		
suggestions 	could, might 	We could try turning it upside down.  You might try giving their hotline a call. 	Why don't (you / we etc.)  How about -ing? 		
emphatic recommendation 	must 	You must see it - it's so funny. 	(You)'ve got to (see it) 		
emphatic invitation 	must 	You must come over to dinner. 			
strong obligation 	must 	I must get these brakes done. 			
mild obligation 	should, ought 	You ought to say sorry. 			
strong prohibition 	mustn't 	You must not touch that. Ever. Do you understand? 	Negative imperative  (Do not touch that_ 		
strong necessity 	must 	We really must stop wasting paper like this. 	It is essential that 		
guess or deduction about the present 	must, should, could, may, might, can't 	She must be asleep - she's not answering her phone.  It should be ready - I put it in the oven an hour ago.  He could / may /might be in the garden.  It can't be Jane. She's gone abroad. 	probably  (I) doubt  It's (un) likely that  It's possible that 		
guess or deduction about the past 	must have, should have, could have, may have, might have, can't have 	Look there's Henry's briefcase. He must have forgotten it.  They should have arrived by now.   He can't have gone home. His bag is still here. 	probably  (I) doubt  It's (un) likely  It's possible that 		
prediction about the future (probability) 	will, may, might, could 	It'll probably arrive tomorrow.  It could rain this afternoon.  I suppose I might change my job one day. 			
a deduction about the future 	should 	He should be here in a minute. He left ages ago. 			
criticism about a past action etc 	could have  should have  shouldn't have 	You could have let me know!  I should have done this earlier.  You shouldn't have put your wallet in your back pocket. 			
future in the past (past of 'shall') 	would, should 	I told him I'd call him  I knew I should be home soon. 			

  
  
1	can / could

  
ability 	criticism 	future prediction (probability) 	guess about the past 	guess about the present 	offer 	permission 	possibility 	request 	suggestion 	

Can you recommend a good grammar reference book? 	request 	
Can I borrow your notes from last week? 		
Can you speak any other foreign languages apart from English? 		
Can I give you a hand with your homework? 		
Can you understand what I'm saying? 		
You can't have finished already. 		
Can't you do it a bit quicker? 		
Could you explain to me the difference between the past simple and the past perfect? 		
Could you read or write before you started school? 		
 Do you think the Americans could have faked the moon landings? 	guess about the past 	
Could I borrow fifty dollars until next week? 		
Could you understand what Alex told us about the past perfect last week? 		
Do you think it could rain later? 		
You could have told me you were having a party! 		
You could try putting some WD40 on it. 		
You absolute pig! How could you?  		
I would if I could but I can't. 		
He could be in his office. Why don't you try calling his work number? 		

  
Can you recommend a good grammar reference book? 	request 	
Can I borrow your notes from last week? 	permission 	
Can you speak any other foreign languages apart from English? 	ability 	
Can I give you a hand with your homework? 	offer 	
Can you understand what I'm saying? 	ability 	
You can't have finished already. 	logical possibility  (guess about the present) 	
Can't you do it a bit quicker? 	request (impatience)* 	
Could you explain to me the difference between the past simple and the past perfect? 	request 	
Could you read or write before you started school? 	ability 	
 Do you think the Americans could have faked the moon landings? 	guess about the past 	
Could I borrow fifty dollars until next week? 	permission 	
Could you understand what Alex told us about the past perfect last week? 	ability 	
Do you think it could rain later? 	future prediction 	
You could have told me you were having a party! 	criticism 	
You could try putting some WD40 on it. 	suggestion 	
You absolute pig! How could you?  	possibility (criticism) 	
I would if I could but I can't. 	ability or possibility** 	
He could be in his office. Why don't you try calling his work number? 	guess about the present 	

 * Questions formed with negatives often have the effect of adding the feeling of the speaker. Here the feeling is impatience. 
** This is a short answer so whether the can and could refer to possibility or ability, depends on the original question. 
'Would you like to come to a party this evening? 
I would if I could but I can't...because I have to work late (possibility: it is not possible for me to come) 
Can you translate this isn't Mandarin for me? 
 I would if I could but I can't...because I can't speak Mandarin (ability) 

  
2	must
  
emphatic invitation 	emphatic recommendation 	guess or  deduction  about the past 	guess or deduction  about the present 	strong prohibition 	strong obligation  to self 	strong necessity 	

Must we really study modal auxiliary verbs? 	strong necessity  / obligation 	
It must be nearly time for a break. 		
The thieves must have got in through the first floor window. 		
It's the best film I've seen for ages. You really must see it. 		
I really must stop eating cakes. 		
You must be joking! 		
You really must come over and see us some time.  		
You must not go into that room under any circumstances. Do I make myself clear? 		
We really must find a way to reduce our fuel costs. 		

Must we really study modal auxiliary verbs? 	strong necessity  / obligation 	
It must be nearly time for a break. 	guess / deduction about the present 	
The thieves must have got in through the first floor window. 	guess / deduction about the past 	
It's the best film I've seen for ages. You really must see it. 	emphatic recommendation 	
I really must stop eating cakes. 	strong obligation to self 	
You must be joking! 	guess / deduction about the present 	
You really must come over and see us some time.  	emphatic invitation 	
You must not go into that room under any circumstances. Do I make myself clear? 	strong prohibition 	
We really must find a way to reduce our fuel costs. 	strong necessity  	

* i.e. Is it really necessary to study modal auxiliary verbs? 

 3	 may and might 
  
guess or deduction about the past 	guess or deduction about the present 	permission 	possibility 	prediction about the future (probability) 	
  
May I have the pleasure of the next dance? 		
You may use the car but you are to return it immediately. Is that understood? 		
Research suggests there may be a link between obesity and some forms of cancer. 		
You may well be right. 		
The kidnappers may have taken her abroad. 	guess or deduction about the past 	
Do you think I might borrow your dictionary for a moment? 		
It might rain. I'd take your brolly if I were you. 		
The pilot might have had a heart attack. 		
He might be in the library. Why don't you call his mobile? 		
Might I have your attention for one moment, ladies and gentlemen? 	permission 	

May I have the pleasure of the next dance? 	permission 	
You may use the car but you are to return it immediately. Is that understood? 	permission 	
Research suggests there may be a link between obesity and some forms of cancer. 	possibility 	
You may well be right. 	possibility 	
The kidnappers may have taken her abroad. 	guess or deduction about the past 	
Do you think I might borrow your dictionary for a moment? 	permission 	
It might rain. I'd take your brolly if I were you. 	prediction about the future (probability) 	
The pilot might have had a heart attack. 	guess or deduction about the past 	
He might be in the library. Why don't you call his mobile? 	guess or deduction about the present 	
Might I have your attention for one moment, ladies and gentlemen? 	permission 	

 4 	should and ought 

  
advice 	criticism about a past action etc 	a deduction about the future 	future in the past (past of 'shall') 	mild obligation 	
 
He should be here in a minute; it's nearly ten fifteen. 	a deduction about the future 	
What should I do about booking a room? 		
The party should be good ; they've ordered loads of food and drink. 	 	
I keep getting chest pains. Do you think I should see a doctor? 		
I can't keep my eyes open. I should've had a nap after lunch. 		
Applications should be sent before 21 December. 		
I knew that I should be home soon. 	future in the past (past of 'shall') 	
He shouldn't have spoken to her like that. It sounded so rude. 	criticism about a past action etc 	
You ought to take more care. 		
I've ordered three bottles of wine. That ought to be enough. 		
They ought to be here by now. I told them that we were starting at seven. 		
We ought to buy her a card at least. She's been here for three years. 		

He should be here in a minute; it's nearly ten fifteen. 	a deduction about the future 	
What should I do about booking a room? 	advice 	
The party should be good ; they've ordered loads of food and drink. 	a deduction about the future 	
I keep getting chest pains. Do you think I should see a doctor? 	advice 	
I can't keep my eyes open. I should've had a nap after lunch. 	criticism about  past action etc 	
Applications should be sent before 21 December. 	mild obligation 	
I knew that I should be home soon. 	future in the past (past of 'shall') 	
He shouldn't have spoken to her like that. It sounded so rude. 	criticism about a past action etc 	
You ought to take more care. 	advice 	
I've ordered three bottles of wine. That ought to be enough. 	a deduction about the future 	
They ought to be here by now. I told them that we were starting at seven. 	a deduction about the future 	
We ought to buy her a card at least. She's been here for three years. 	mild obligation